Compensating system for presses



Oct. 15, 1957 H. B. ALBERS 2,809,542

COMPENSATING SYSTEM FOR PRESSES Filed Feb. 17, 1953 3 Sheets-Sheet 1 PRESSURE SOU CE H. B. ALBERS 2,809,542

COMPENSATING SYSTEM FOR PRESSES Oct. 15, 1957 3 Sheets-Sheet 2 Filed Feb. 1'7, 1953 Oct. 15, 1957 H. B. ALBERS COMPENSATING SYSTEM FOR PRESSES 3 Sheets-Sheet 3 Filed Feb. 17, 1955 2,809,542 Patented Oct. 15, 1957 cor/mENsA'rnso SYSTEM non PRESSES Heinrich B. Alhers, Malverne, N. Y., assignor, by mesne assignments, to Ealdwin-Lima-Hamilton Corporation, Philadelphia, Pa, a corporation of Pennsylvania Applicahlon February 17, 1953, Serial No. 337,375

9 (Iiaims. (Cl. 73-42) This invention relates to presses and the like in which a plurality of members are relatively movable towards each other to develop high pressures therebetween. The invention is particularly adapted for die forging presses having a moving platen and a fixed platen, in which a workpiece is shaped by the pressure developed between the dies carried by the platens. In such presses eccentric loading conditions are frequently encountered and, because of the hi h pressures developed between the platens, correspondingly high eccentric forces are developed which tend to tilt the movable platen and thus may cause serious damage to the major components of the press, particularly to the columns or tie-rods which would be subjected to severe bending stresses.

it is the principal object of this invention to provide improved means for automatically counteracting or compensating for the stresses developed by eccentric loading of a press and the like of the type described above.

Heretofore, it has been proposed to provide such compensation with the aid of double-acting return pistons which are carried by the moving platen and operate in return cylinders filled with liquid. If the moving platen tilts due to an eccentric load, one of the return pistons will travel faster and the arrangement is such that liquid will be pumped from the cylinder having the faster moving return piston into a cylinder having a slower moving return piston. Since the return cylinders must be capable of accommodating their pistons throughout the entire stroke of the moving platen, these cylinders are relatively long and contain a large amount of liquid. Due to the compressibility of liquid, the larger the amount of liquid to be compressed the slower will be the response of the compensating device.

it is therefore a further object of this invention to provide a compensating system employing pistons or rams which do not move relative to their cylinders during the entire movement of the platen but only during the final movement thereof when it is substantially in engagement with the work-piece. This arrangement permits the use of short cylinders and a corresponding small quantity of liquid with a small degree of compression movement to stabihze the press within narrow limits of tilt.

in compensating systems for hydraulic presses heretofore proposed, the liquid employed in the compensating system was part of the main hydraulic system utilized in operating the press. It is another object of the invention to provide a compensating means in which the hydraulic system employed therein is separate from the hydraulic system which operates the press. This permits the use in the compensating system of a more expensive liquid with a lower compressibility coeificient, which will assist in reducing the required compression movement further so that the response of the system to tilting movement will be still faster. This is important in presses of high capacity and large dimensions.

As described above, prior compensating systems transferred liquid from one side of the system directly to the other side. it is another object of this invention to provide a hydraulic compensating system wherein there is no direct transfer of liquid from one side to the other, permitting the use of single-acting pistons or rams.

Further objects and advantages of this invention will become apparent in the following detailed description thereof.

In the accompanying drawings,

Fig. l is a diagrammatic view, partly sectioned vertically, showing the compensator elements applied to a closed die forging press of which only certain parts such as the platens and the dies supported thereby are shown, the compensator pistons being in their upper positions.

Fig. 2 is a front view, partly sectioned vertically, of the pressure element of the compensating system, the pistons being in their lower positions.

Fig. 3 is a section taken substantially along the line 33 of Pig. 2.

Fig. 4 is a vertical section through one of the stops on the movable platen, showing a modified arrangement on a large scale.

Fig. 5 is a diagrammatic plan View showing the arrangement of a plurality of compensating units arranged along predetermined axes.

Fig. 6 is a vertical diagrammatic section generally corresponding to Big. 2, but showing a plurality of pressure elements having a single stationary framework, the pistons being intheir upper positions.

Referring to Fig. 1, the invention is shown applied to a closed die forging press having a fixed platen l0, and a moving platen 11 which is adapted to be moved toward the fixed platen by means of rams 12 actuated by fluid pressure from a source indicated diagrammatically. The upper platen carries an upper die 14 which moves toward the lower die 15 on the fixed platen, the work piece 36 to be forged being supported on the lower die. The upper platen l'l moves normally parallel to the fixed platen ill by reason of the construction of the press which is provided with suitable guide members (not shown), but when the upper die engages the work piece, particularly when the die or the work piece is of irregular shape, the upper platen may he tilted out of parallelism with the lower platen. As stated in the introduction hereto, such tilting movement due to eccentric loading conditions develops large stresses in certain of the major components of the press, and especially in the columns or tie-rods which are subjected to severe bending stresses.

in order to prevent such large eccentric loading stresses from developing in the press, there is provided the compensating mechanism disclosed in Fig. 1. This mechanism comprises essentially a plurality of inclination responsive elements generally indicated at A, A and mounted in the press, and a pressure element generally indicated at G normally mounted on the foundation adjacent to the press. These elements A, A and G cooperate with each other. As shown in the drawing, each of a pair of cylinders 2i) and 2h accommodates a piston or ram 21, 21 which is supported on a body of liquid 22, 22 supplied through pipes 23, 23 from fluid 24, 24 contained within fixed cylinders 25, 25'. The fluid within cylinders 25, 25 is contr d by pistons or rams 26, 26 which are part of a reciprocable fram work F comprising crossheads 3%, 36' and tie rods 31. "l he framework F also carries an additional piston 32 which is movable within a fixed cylinder 33, said piston 32 being supported by fluid supplied from a primary source of fluid pressure such as an accumulator (not shown) through a pipe 34. The fured cylinders 25 and 33 may be parts of one integral piece which, as illustrated in Figs. 2 and 3, may be mounted in a base 36 supported on the foundation. The base 36 is part of a stationary framework comprising tie rods 35 and upper crossheud in which the fixed cylinder 25 is mounted. Openings 39 in base 36 accommodate and guide the moving tie rods 31 of reciprocable framework F.

Pistons 21, 21' are of equal diameter, and pistons 26,

26 are of equal diameter. The size of piston 32 will depend upon the accumulator pressure which is normally relatively high. When no load is applied to the upper faces of pistons 21, 21, a low ressure is maintained in lines 23, 23 from a source of pressure (not shown) through check valves 37, 37' which are adapted to open when the pressure in lines 23, 23 falls below a predetermined value. Thus the accumulator pressure may be on the order of 4000 p. s. i. whereas the pressure in cylinders 20, 20 when no load is applied to the upper faces of pistons 21, 21 may be on the order of 100 p. s. i. Stroke limits (not shown) are provided to limit the upward movement of framework F and of pistons 21, 21. In case of losses due to leakage, lines 23, 23 are automatically replenished with fluid through valves 37, 37 when the latter'open upon a drop in minimum pressure. Examining the structure as described above, it will be seen that the framework F is normally supported on the accumulator fluid under pressure and that each of the pistons 21, 21 rests upon this framework by its own separate hydraulic system, each side of the compensator being hydraulically independent of the other side. It will also be apparent that the fluid pressure systems between pistons 21, 21 and the framework F are separate from the main hydraulic pressure system which operates on rams 12 to move the movable platen toward the fixed platen.

Bearing the foregoing facts in mind, the operation of the device asv a compensating mechanism to counteract eccentric loading of the press will now be described. Contact members or stops 46 and 40' carried by the upper platen near its outer edges are adjustable so that normally these stops will just engage pistons 21, 21' when the upper die 14 is about to engage the work piece 16, or when it is substantially in engagement with the work piece, that is, when substantial forces are developed. In other words, the pistons 21, 21 are disconnected from the upper platen until the upper platen has substantially completed the idle part of its stroke. Thereafter further downward movement of the platen will cause stops 4%, 40' to press against both pistons 21, 21 with equal pressure if there is no eccentricity, and pistons 25, 26' will be forced downwardly to force piston 32 downwardly and discharge fluid into the accumulator, the main rams 12 being large enough to overcome the additional resistance. Since pistons 21, 21'

, are of equal size, and pistons 26, 26' are also of equal size, the pressure in lines 23, 23 will be equal. It will further be clear that the sum of the forces exerted by pistons 26, 26 will be equal to the force required to move piston 32 downwardly against the accumulator pressure. Thus during concentric forging, each of the pistons 26, 26' supplies one half of the force exerted on piston 32.

Assume now that as the upper die engages the work piece, eccentric loading of the upper platen develops and the right hand end moves downwardly more rapidly than the left hand end. The tilting of the platen is thus in a clockwise direction in the drawing, and greater pressure will be exerted on piston 21 than on piston 21. The pressure in line 23 will rise and piston 26 will furnish an increased share of the force exerted on piston 32. This will relieve piston 26 correspondingly and the pressure in line 23 will also drop to a corresponding value, resulting in a decrease in force at piston 21. In other words, there will be a diiferential'force between pistons 21, 21 which will create a moment acting on the upper platen in a cotinter clockwise directionandcounteracting the tilting motion so that the platen will again be brought into a straight position. Similarly, increased pressure on piston 21 would cause the platen to move in a clockwise direction if the eccentricity originally caused the platen to move in a counter-clockwise direction; 7 V

Separate return cylinders (not shown) are provided for the return stroke of the moving platen 11. When platen 11 performs its return movement, the accumulator pressure acting on piston 32 will cause framework F to move upwards, and the fluid expelled from cylinders 25, 25' will lift the pistons 21, 21. At the start of the return stroke of platen 11, pistons 21, 21' may assist in lifting the platen and in separating the workpiece from the die.

As shown in Fig. 4, the stops 40, 49' may be adjusted in position relative to platen 11 by means such as reversible motor 50 driving through gearing 51 to rotate the stop which has screw-threaded engagement with a fixed sleeve 52.

The structure described in Fig. 1 comprises a single compensating unit, but it will be apparent, as shown in Fig. 5, that a plurality of such units may be employed along selected axes of the moving platen by multiplication of the elements disclosed in Fig. 1, i. e. the cylinders 20, 29, their pistons 21, 21, stops 40, 4%), pressure element G, and the hydraulic connections 23, 23. The arrangement according to Fig. 5 comprises three units. In this embodiment, the moving platen 60 has a rectangular shape. Cylinders 20, 20' are located in a transverse plane in the center of the press and are connected to pressure element G so that they operate in the same manner as described hereinbefore. A second pair of cylinders 61, 61' are positioned adjacent respective diagonally opposite corners of the platen and connected to a second pressure element H, while a third pair of cylinders 62, 62 are located adjacent the remaining corners of the platen symmetrically to the other cylinders, cylinders 62, 62 beingconnected to a third pressure element 1. It will be clear that any tilting of the platen about axis X--X will be counteracted by cylinders 61, 61' and 62, 62, and any tilting about axis YY by all the cylinders. Further, any tilting about the approximately diagonal line V-V will be counteracted by cylinders 61, 61 and 20, 20 and any tilting about the approximately diagonal line W--W by cylinders 62, 62' and 20, 2%. Intermediate tilting movements will be counteracted by a corresponding combination of cooperating cylinders.

As diagrammatically shown in Fig. 6, several pressure elements of the type G, H, I may be combined so as to form a common stationary framework, comprising a base resting on the foundation, tie rods 71, and an upper crosshead 72. In the embodiment shown, three reciprocable frameworks F are arranged in the stationary framework and are movable independently from each other to cooperate with pairs of cylinders such as 28 and 20,61 and .61, 62 and 62' shown in Fig. 5.

Since the stops 40, 40 of the upper platen do not engage pistons 21, 21'until the actual forging stroke starts, it is possible to make the cylinders 20, 25 and 20, 25' relatively short so that relatively little fluid is contained in each fluid system 22, 23, 24 and '22, 23, 24'. This means that very effective compensation can be obtained because of the small degree of fluid compression. above systems are separate from the main hydraulic system'and this permits the use of relatively expensive fluid such as glycerine, with a low compression coefficient, which will further assist in obtaining effective and rapid compensation.

Various details of construction may be modified within the scope of the invention as defined in the appended claims. For example, the stops 40, 4% maybe attached to the fixed platen, and cylinders 20, 20 may be mounted on the moving platen, the movement of pistons 21, 21' in their cylinders 20, 20 being limited by suitable means. Furthermore, the cylindersZt), 20 and stops 40, 40 may be attached to the side faces of the platen.

Having described my invention, what I'claim and desire to secure by Letters Patent is 2 1. In a hydraulic press having a fixed platen, a platen mounted for movement along a predetermined axis and having a stroke including an approach range and a working range, one of said platens being adapted to support:

In addition, the

a workpiece thereon, and means for compensating for tilting movement of said movable platen relative to said predetermined axis by generating a movement of said movable platen opposite in direction to said tilting movement, the improvement in said compensating means which comprises; hydraulic cylinder and piston units mounted on one of said platens and having a stroke substantially equal to the length of said working range of the stroke of the movable platen, and contact means on the other platen spaced from said hydraulic units at the start of said stroke so as to engage said hydraulic units at a predetermined position of the movable platen substantially only within said working range of the stroke.

2. The combination as specified in claim 1, in which the cylinder and piston units are mounted on the fixed platen.

3. In a hydraulic press having a fixed platen, a platen mounted for movement along a predetermined axis and having a stroke including an approach range and a working range, one of said platens being adapted to support a workpiece thereon, and means for compensating for tilting movement of said movable platen relative to said predetermined axis by generating a movement of said movable platen opposite in direction to said tilting movement, the improvement in said compensating means which comprises at least one pair of cylinder and piston units mounted on one of said platens on opposite sides of said predetermined axis and having a stroke substantially equal to the length of said working range of the stroke of the movable platen, said units being operated by hydraulic pressure, contact means on the other platen spaced from said pair of hydraulic units at the start of said stroke so as to engage said hydraulic units at a predetermined position of the movable platen substantially only within said working range of the stroke, and means for decreasing the hydraulic pressure in one of said units when the hydraulic pressure is increased in the other of said units due to tilt of the movable platen.

4. The combination as specified in claim 3, including a source of hydraulic pressure for operating the movable platen, and an auxiliary hydraulic pressure system for each of said units, said auxiliary hydraulic pressure systems being separate from said source of hydraulic pressure for operating the movable platen.

5. The combination as specified in claim 3, including a second pair of cylinder and piston units coordinated to the first-mentioned pair of units, and a fluid connection between each cylinder of the second pair and the respective cylinder of the first pair.

6. The combination as specified in claim 5, in which the pistons of the second pair operate as a unit.

7. The combination as specified in claim 6, which includes a third piston movable as a unit with said second pair of pistons, a cylinder for the third piston, a source of primary hydraulic pressure, and a fluid connection leading from the source of primary hydraulic pressure to said cylinder for the third piston.

8. The combination as specified in claim 7, in which the cylinders for the second pair of pistons and for the third piston are fixed in position.

9. In a hydraulic press having a med platen, a platen mounted for movement along a predetermined axis and having a stroke including an approach range and a working range, one of said platens being adapted to support a workpiece thereon, and means for compensating for tilting movement of said movable platen relative to said predetermined axis by generating a movement of said movable platen opposite in direction to said tilting movement, the improvement in said compensating means which comprises at least one pair of hydraulic cylinder and piston units mounted on one of said platens on opposite sides of said predetermined axis and having a stroke substantially equal to the length of said working range of the stroke of the movable platen, adjustable contact means on the other platen spaced from said pair of hydraulic units at the start of said stroke so as to engage said hydraulic units at a predetermined position of the movable platen substantially only within said Working range of the stroke, a source of hydraulic pressure for operating the movable platen, a separate auxiliary hydraulic pressure system for each cylinder and piston unit, the fluid in the auxiliary hydraulic pressure systems having a coeflicient of compressibility which is low relative to the coefficient of compressibility of the fluid for operating the movable platen, and means for decreasing the hydraulic pressure in one of said auxiliary systems when the hydraulic pressure is increased in the other of said systems due to tilt of the movable platen.

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